The use of a hydrophilic membrane to provide moisture to a growing medium and/or to irrigate plants is known. WO-A-99/40031, for example, discloses a method for providing moisture to a growing medium wherein water vapour passes through a non-porous hydrophilic membrane via the process of pervaporation. The hydrophilic membrane is made from a hydrophilic polymer such as a copolyetherester elastomer, polyether-block-polyamide, polyether urethane, or polyvinyl alcohol. In one embodiment disclosed in this document the membrane forms a container that is buried in the growing medium. The container is provided with water and the water then passes through the membrane and is transmitted into the growing medium as water vapour via the process of pervaporation. Contaminated water can be used in the methods disclosed in this document since the hydrophilic membrane limits the passage of contaminants into the growing medium.
Similarly, WO-A-01/10192 discloses an irrigation device comprising a container for water wherein the container comprises a hydrophilic membrane and one surface that is impermeable to water in all forms. The container can be completely buried in a growing medium. WO-A-01/10193 discloses a method for modifying plant root growth wherein plant roots are grown in close proximity to a hydrophilic membrane which releases water as the roots grow. The membrane can be in the form of a sealed cylinder that is buried in the growing medium and connected to a water source.
In all of the above systems the container formed from the hydrophilic membrane is sealed in order to prevent leakage of contaminants into the growth medium and/or to allow close control of the supply of water to the growth medium. If the membrane had any holes, or if the membrane ruptured during use, contaminants would leak into the growing medium and water would leak out of the container and flood the growing medium.